This invention relates to lasers, and in particular to a mirror system for controlling a laser beam such as a collimated annular beam.
Practical commercial usage of lasers in commercial applications is in large measure dependent upon developing economic and dependable laser beam sources of sufficient power, and suitable peripheral equipment in the form of optical systems to focus and control the laser beam. Optical systems for focusing and controlling laser beams have been developed which use mirrors for focusing and controlling the beam. One such system uses an axially symmetric Cassegranian telescope for this purpose. With this axially symmetric system, the laser beam from a source which is typically in the form of a collimated annular beam enters the rear of a tubular telescope housing through an opening in a forwardly facing concave mirror and impinges on a centrally disposed rearwardly facing convex mirror. The beam is reflected back to the concave mirror, where it is reflected forwardly and out of the housing to a point of focus. Unfortunately, this type of system has disadvantages in requiring support structure for mounting the convex mirror which interferes with the laser beam.
In an attempt to at least partially avoid this problem, improved right angle Cassegranian systems have been developed such as shown in U.S. Pat. No. 3,907,408 to Engel, assigned to the assignee hereof. With this right angle Cassegranian system the intersecting support struts are eliminated. However, this right angle system requires three mirrors. Since the mirrors absorb power of the laser beam, this is disadvantageous over the axially symmetric Cassegranian telescope which requires only two mirrors. The additional mirror also adds to the complexity of the system since it requires extra mounting structure and extra cooling structure to take away heat generated in the mirrors.
To solve these and other problems, mirrors have been proposed which use complex shapes such as parabolic shapes. The present invention provides a variable focus off axis parabolic mirror system, as will be hereinafter described.